Delivery of enhanced services in cellular telecommunications systems has become commonplace and serves to differentiate cellular providers in the marketplace. These enhanced services include 800 Services, Geographic Call Routing, Flexible Call Routing, Flexible Carrier Selection, CLASS Services, and Single Number Service. These services are typically of the number translation type, which involves accessing a database through a Service Control Point (SCP) and retrieving call processing information that is used to forward a call to the desired final destination.
Most cellular systems now support the Signalling System 7 (SS7) Integrated Services Digital Network User Part (ISUP) call control protocol, as described in American National Standards Institute (ANSI) standard T1.113-1995, "Signalling System Number 7 (SS7)--Integrated Services Digital Network (ISDN) User Part," 1995, New York, N.Y., hereby incorporated by reference.
One system for delivering enhanced services in an ISUP network is described in U.S. Pat. No. 5,377,186 to Wegner, et al. The system uses a Local Switch (LS) connected through the network to a SCP wherein a subscriber services database resides. The LS is provisioned for ISUP. A number of loop-back trunks with defined Circuit Identification Code (CIC) pairs are also provisioned on the LS. The routing table in the LS is modified to route the voice signal for calls requesting the enhanced subscriber service to the outbound connection of one of the loop-back trunks, and to route to the SCP the associated ISUP messages. The SCP is modified so that an ISUP interface will perform limited switch-type functions, e.g., number translation, using parameters in the ISUP call-setup messages that were originally intended for conditions such as call forwarding. To the network, the SCP appears to be a switch.
When a call requesting the enhanced user service is received by the LS, an ISUP Initial Address Message (IAM) is routed to the SCP and voice is directed to the CIC of the outbound connection of a loop-back trunk. When the SCP receives the IAM message, the ISUP interface treats the IAM message as a query message requesting retrieval of a subscriber service. The SCP responds to the query and returns a new routing number, or translated destination, for the call. The ISUP interface generates an IAM(Call-Forward) message that includes the new routing number and the CIC of the inbound connection of the loop-back trunk. The IAM(Call-Forward) message is then sent back to the originating LS directing the LS to initiate a new call to the translated destination. Thus the original call is connected to the translated destination via the loop-back trunk, which remains in the circuit for the duration of the call. As well, the SCP remains in the signaling path of the call and appears to control a voice circuit segment that connects the outbound portion of the loop-back trunk to the inbound portion of the loop-back trunk. The concepts in the invention described in the patent to Wegner, et al., may generally be applied to cellular radio telecommunication systems by incorporating the suggested changes to the LS into a Mobile Switching Center (MSC) of a cellular system in an SS7/ISUP network.
The approach described by Wegner, et al., works well for enhanced services of the number translation type that require a single hop??? to a SCP before connection to the final destination. However, there are enhanced services in an ISUP network that require a connection to an intermediate end-point destination followed by a connection to a final destination. For example, in the preferred embodiment of the present invention, a caller is first connected via a SCP to an interactive voice response unit (IVRU) residing on a separate network element, in the manner of Wegner, et al., that can, for example, give status of the caller's enhanced services account. After interacting with the IVRU, this connection is dropped and the caller is then connected via the SCP, again in the manner of Wegner, et al., to the final destination. In the embodiment, the SCP stays in the circuit.
In the standard ISUP protocol, this enhanced service would be difficult to implement because ISUP protocol calls for the complete end-to-end tear down of a call upon a release generated anywhere in the connection. It is desirable to release only a portion of the established circuit segments while maintaining the rest, for example, only those segments from the intermediate end destination back to the SCP, and then to extend the maintained segments to a new destination.
Accordingly, it is an object of the present invention to provide a method in an ISUP network that will allow a connection to an intermediate destination followed by a connection to a final destination without complete call tear down upon release of the intermediate circuit, thus allowing a SCP to remain in the circuit for the complete duration of all connections.